Operator workload is driven by three main topics:
- The physical equipment they monitor.
- The interactions they do on a day-to-day basis.
- The automation system.
If you want to influence the workload you must make changes to one of these three areas of influence. The easiest one to comprehend is the physical equipment under their control. The equipment is broken down into one of five complexity boxes. The first and most simple box is designated as equipment that stores products, for example, an oil tank. We add a complexity rating to every type of storage tank, vessel, drum etc.
The complexity rating is derived from four influences, so we look at four areas People, Information, Technology, and Materials. The type of worker and the education and training required to monitor and control it. For example, the complexity of a storage tank with simple instrumentation for level control and pressure is minimal and does not need rocket science to work with it.
The technology is limit compared to a reactor. The information flow is less than a reactor, change is at a minimum for storage compared to a reactor, and the error rates and speed of operations are a lot less for storage than a reactor.
Between storage and reaction which is where the product being made is transformed from raw materials to a product where a transformation takes place. While storage does nothing to the product or raw material it simply holds it.
We rate equipment and the complexity of equipment into five groups, storage, transfer, cosmetic changes, supplemental transformation and full transformation and every piece of equipment on a P&ID is scored based on these levels.
A total mechanical score is obtained and is additive to our workload scoring system.
Interactions come in many forms from sharing a common utility such as steam, electricity, H2, etc. If one unit rocks the header communications and collaboration are required or the whole system could potentially shut down. We count communications as an interaction some face-to-face and others over radios and phones. If an operator spends 4 hours on the phone per shift that is a significant reduction in time available to do other duties.
The automation section looks at several variables, how much of the process is automated and how much is still under manual control which would require coordination and communications with an outside operator. Sometimes, equipment was automated but the operator chose to keep a control on manual for ease of operations. This again is additional work and was not intended in the design of the automation.
The automation system can also generate work for an operator, for example, a poorly designed alarm management system can become a real burden and high workload item for an operator.
Bad HMI design can also burden an operator if they must navigate across several graphic pages just to make a simple corrective action.
If the workload is higher than preferred or is not sustainable at the current levels the only ways to reduce workload are to redesign the boundaries of the equipment and move some to another operator, or if the workload is low add more equipment.
It may also be possible to increase and improve the automation to reduce workload, for example, an alarm rationalization study can significantly reduce operator workload dependent on the state of the alarm system. We had one alarm system that was using 6 hours per shift of an operator’s time based on just spending an average 30 seconds per alarm.
Doing phone surveys can identify unnecessary distractions and lost time for a control operator, also looking at other duties and removing unnecessary duties can reduce workload and fatigue. A good example is an operator is required to schedule overtime and it takes 2 hours a day to schedule and contact other operators, moving this to a clerk can dramatically impact an operators day.